1. Field of the Invention
The present invention relates to a developing unit comprising a developing member such as a developing roller that contacts an image support member such as a photosensitive drum charged at a predetermined electric potential and supplies the image support member with liquid developer, and an image forming device comprising the developing unit.
2. Background Information
An image forming device having a developing unit therein that is comprised of a developing roller that contacts a photosensitive drum charged at a predetermined electric potential and supplies the photosensitive drum with liquid developer, and a supply roller that supplies the developing roller with the liquid developer, has been known as a so-called wet image forming device that is typified by a multifunction device and a printer device and performs image formation with liquid developer. In this type of image forming device, the photosensitive drum and the developing roller are in contact with each other. Therefore, even if the photosensitive drum is not charged at a predetermined electric potential, liquid developer attached to the developing roller may still be supplied to the photosensitive drum. Basically, the supply of liquid developer to a portion of the photosensitive drum that is not charged at a predetermined electric potential is unnecessary, and wastes liquid developer.
Japan Patent Application Publication JP-05-173410 discloses a technique for preventing the supply of developer to a photosensitive drum by suspending the driving of a developing roller when the supply of developer to the photosensitive drum is unnecessary (e.g., before image formation). On the other hand, Japan Patent Application Publication JP-2002-287516 discloses a mechanism for separating a developing roller from a photosensitive drum. It is thought that this mechanism will prevent the supply of developer to the photosensitive drum when it is unnecessary.
However, with the technology disclosed in Japan Patent Application publication JP-05-173410, the photosensitive drum is driven while the photosensitive drum contacts the suspended developing roller. Therefore, the photosensitive drum slides in contact with the developing roller, and accordingly the photosensitive drum will become scratched. On the other hand, in a configuration in which the developing roller is repeatedly forced to separate from the photosensitive drum, deviation in the positional relationship between the developing roller and the photosensitive drum will easily occur. Accordingly, this positional deviation will cause deterioration in developing performance.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved developing unit that can prevent waste of liquid developer by blocking the unnecessary supply of liquid developer to an image support member, and prevent deterioration in developing performance caused by damage to the image support member and positional deviation of the developing member (e.g., a developing roller and the like), and an image forming device comprising the same. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.